Showing papers by "Wilko Wilkening published in 2007"

Feasibility of contrast-enhanced sonography during resection of cerebral tumours: initial results of a prospective study.

Abstract: The aim of this study was to adapt the ultrasonographical techniques developed for brain perfusion imaging to an intraoperative setting for topographic diagnosis of cerebral tumours During surgery, the patients underwent contrast-enhanced ultrasonography (phase inversion harmonic imaging, bolus kinetic, fitted model function) Endocavity curved array (65EC10, 65 MHz) was used intraoperatively The ultrasound contrast agent SonoVue (Bracco) was administered IV as a bolus injection Off-line, time-intensity curves as well as perfusion maps were calculated and parameters such as peak intensity were locally extracted to characterise perfusion Seven patients with brain tumours of different histologic types were subjected to contrast-enhanced ultrasonography during surgery Tissue differentiation with contrast agent was superior to conventional B-mode ultrasound imaging Intraoperative contrast-enhanced ultrasonography enabled visualisation of cerebral tumours in high spatial resolution

Intraoperative ultrasound using phase inversion harmonic imaging: first experiences.

Abstract: Objective To study the feasibility of intraoperative ultrasound using the phase inversion harmonic imaging (PIHI) technique. Methods Eight patients with intracranial middle cerebral artery aneurysms and five patients with arteriovenous malformations were studied after written informed consent. A first ultrasound study was performed through the intact dura mater after cranial trepanation to assess the pathology, its feeding artery, and downstream segments. A second ultrasound study was performed immediately after intervention to monitor the success of the procedure. All patients were studied using a Siemens Sonoline Antares ultrasound machine (Siemens Medical Solutions USA, Inc., Malvern, PA) before and after intravenous administration of an ultrasound contrast agent (Optison; GE Healthcare, Milwaukee, WI). Other than conventional brightness mode, PIHI is sensitive to the nonlinear acoustic response of tissue, and especially to ultrasound contrast agent microbubbles. The latter enables contrast-specific vascular imaging. Results PIHI provided anatomically detailed information. In combination with an ultrasound contrast agent, angiography-like views of the vascular pathologies, including their surrounding vessels, could be obtained. Flow velocities in afferent and downstream vascular segments, as well as inside the pathology, could be assessed. Flow dynamics inside the aneurysm sac or the arteriovenous malformation could be studied in real-time. Postintervention, contrast-enhanced PIHI could be used to immediately monitor the success of the surgical procedure. Conclusion PIHI enables intraoperative visualization and morphological assessment of neurovascular pathologies, such as middle cerebral artery aneurysms or arteriovenous malformations. In combination with an ultrasound contrast agent, the flow dynamics of these lesions can be displayed in real-time.

9C-2 Reconstruction of Speed of Sound for a Correction of Transit Time in Full Angle Spatial Compounding

Abstract: For full angle spatial compounding, an object is imaged in one plane from multiple aspect angles and the obtained images are superimposed in correct geometric orientation. Thus, information about the distribution of speed of sound inside the object is required for a correction of individual images with respect to transit time and refraction of the ultrasonic waves. In this paper, we present a method to reconstruct such a distribution by a filtered backprojection of echo data from a reflector positioned behind the object. Using the reconstructed distribution, individual ultrasound images were corrected by a ray tracing algorithm before spatial compounding. Here, refraction was only accounted for at the outer boundary of the object, while inside only transit time was corrected. In vitro analyses are presented that prove the applicability of this approach.

Real-time cerebral angiography: sensitivity of a new contrast-specific ultrasound technique.

Abstract: BACKGROUND AND PURPOSE: To test a new contrast-specific sonography imaging method that offers visualization of the intracranial vasculature in a manner similar to that seen on angiography. MATERIALS AND METHODS: Thirty patients (35 sonography studies total) were included in the study after they provided written informed consent. The patients were scanned through the temporal bone window from both sides after intravenous injection of an ultrasound contrast agent (UCA; perflexane lipid microspheres [Imagent]). The goal was to visualize the intracranial arteries, including the middle (M1–M3), anterior (A1 and A2), and posterior (P1–P3) cerebral arteries, using an axial scanning plane. The studies were performed using a contrast-specific imaging mode, based on a phase inversion technique (transcranial ultrasound angiography [tUSA]). For sensitivity, the results were compared with x-ray angiography as the “gold standard.” For interobserver reliability, 24 of 35 sonography studies were evaluated by 2 physicians with little training in transcranial sonography and by a seasoned sonographer. RESULTS: The sensitivity of tUSA ranged between 0.778 (95% confidence interval [CI] of 0.577–0.914) and 0.963 (95% CI of 0.810–0.999). The sensitivities were similar among physicians with little training in transcranial sonography and the seasoned sonographer, indicating high inter-rater reliability. Overall, tUSA provided high anatomic resolution and vascular delineation even of small vessels in the millimeter range. At peak intensity, no UCA-related artifacts were observed. CONCLUSION: tUSA provides images of the intracranial arteries similar to those obtained at angiography with high anatomic resolution, reasonable sensitivity, and interobserver reliability.

Ultrasonographic contrast-agent imaging of sub-millimeter vessel structures with spatial compounding:in vitroanalyses / Kontrastmittelgestützte Ultraschallabbildung von Sub-Millimeter-Gefäßstrukturen mittels Spatial Compounding:In-vitroAnalysen

Abstract: In clinical diagnostics, ultrasonographic contrast-agent imaging gives access to medical parameters such as perfusion and vascularization. In addition to the artifacts that are typical for ultrasonic imaging, e.g., speckle noise and depth-dependent sensitivity and resolution, contrast-agent imaging shows more pronounced depth dependence and may suffer from shadowing artifacts that arise from high attenuation of the ultrasound waves by the contrast agent at high concentrations. By imaging an object from different viewing angles in one 2D image plane and summing the images obtained (spatial compounding), image quality can be increased and artifacts can be suppressed. In the present study, we combined both techniques to overcome the limitations of contrast-agent imaging. We used a commercially available ultrasound scanner and a custom-made high-precision mechanical system to rotate the ultrasound transducer fully around the object under investigation. Using this set-up, ultrasound data were acquired in reflection mode to generate a 360 degrees compound scan of a flow-mimicking phantom supplied with contrast agent.

P5B-1 A Fast Method for Data Acquisition in Contrast Replenishment Analyses

Abstract: For sequential perfusion measurements in several image planes with replenishment method, we propose a fast technique by consecutively scanning respective image planes twice: Firstly using only a short period of imaging pulses after micro- bubble destruction to assess slope and secondly using few imaging pulses to assess final value. Both scans are combined to extract perfusion rate and blood volume.